For certain diagnostic assays, for example influenza and many sexually transmitted diseases, a clinician would ideally require immediate or very rapid test results to be obtained. This may be for public health reasons to minimise the spread of infection, and to ensure rapid therapeutic treatment for the patient. In remote locations, there may not be a clinical pathology infrastructure near the point of testing, and delays in obtaining test results for some infections could be harmful or even life-threatening to the patient, as well as harmful to the general public.
Rapid tests are available for many medical conditions, and may be procured at low cost. These tests are typically referred to as lateral flow tests, also known as lateral flow assays, membrane based assays, and lateral immunochromatographic tests.
Such tests are traditionally composed of a variety of materials overlapping onto one another and mounted on a backing strip. When a test is run, a sample containing a suspected antigen is added to a sample application pad. The sample migrates to a conjugate pad, where a particulate labelled conjugate specific to the target has been immobilized. The sample remobilizes the conjugate, and the analyte in the sample interacts with the conjugate as both migrate along a porous membrane. A capture reagent, having been laid down in a strip on the membrane at a test line location, serves to capture the analyte and conjugate as they migrate past. Accordingly, if the suspected antigen is present, a visible test line appears.
Whilst such tests offer rapid results, a problem with lateral flow tests is that a significant amount of the antigen or antibody must be present in the sample analyte in order for the development of a visible line. Consequently, these types of tests have a poor degree of sensitivity, resulting in a substantial number of false negative results, especially when a patient is in the early stages of an infection, and when the amount of a particular antigen, antibody or viral load in a patient may be low. Moreover, it is in the early stages of detection that it is important that diagnosis is correctly performed in order to administer an appropriate therapeutic to the patient, or to quarantine the patient to prevent the further spread of the infectious disease to the remainder of the community.
To address this problem, some manufacturers have developed lateral flow tests that employ fluorescent labels to facilitate the detection of an analyte along with appropriate readers. Although these labelling techniques can yield several orders of magnitude increase in sensitivity improvement relative to previous techniques, the complex and often expensive readers required for fluorescent detection have limited the market for such tests. The high cost of such readers detracts from the main benefit of lateral flow testing, which is that it is based on a low cost, robust and easy to use system.
One type of fluorescent reader previously developed for scanning the fluorescent response of an immunoassay performed in a micro titre plate (MTP) is disclosed in U.S. Pat. No. 4,626,684 (the Landa patent). This patent teaches a scanning optical fluorescent reader comprising illumination for exciting a plurality of immunoassay samples in combination with a fluorescence emission analysing means. In the Landa patent, the MTP can be driven by a motion system in one direction with the fluorescent scanner head driven by a motion system in an orthogonal direction, thereby providing bi-axial scanning motion capability. The problem with such scanning type readers is that the scanning mechanism adds unwanted cost and complexity to the reader, with the risk of component failure or in-field maintenance issues due to moving parts. Furthermore, if the scanning system is bumped or dislodged, positional errors can arise thereby affecting the accuracy of the assay.
An imaging optical reader is another kind of optical reading device, which is capable of detecting a two-dimensional array on a substrate. The imaging optical reader comprises an exciting light source, e.g. a xenon lamp, for illuminating a large part of the surface area (or the entire surface area) of the substrate, and a detector capable of detecting emitted light from the entire detection site-area simultaneously. An example of such an optical reader is a CCD (Charged-Coupled Device)-imager, which offers high quantum efficiency, sensitivity and spatial resolution. Further, a wideband light source may be provided with wavelength filters to provide monochromatic radiation. Such fluorescent imaging optical devices have been used in some fluorescent microscopy systems using confocal imaging approaches. These fluorescent optical imaging devices typically employ a range of high-cost thin-film interference filters (TFIFs) for filtering of the excitation light, and for filtering the emitted fluorescent light from the sample. Typically, filter sets used include an excitation filter for the light source, a dichroic mirror or beam splitter (where confocal imaging arrangements are used), and an emission filter for the emitted fluorescent light.
It is desired to address or ameliorate one or more shortcomings or disadvantages associated with prior systems and devices for reading diagnostic assays, or to at least provide a useful alternative thereto.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.